http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53900
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-01-07 04:25:38 UTC --- > __attribute__((aligned(16))) float array[4]; Explicitly says the array is aligned to 16 bytes which means it is undefined by the C/C++ standard what happens if you a pointer to the struct which contains this array. As this pointer will always be aligned by definition of the struct (and any other use of it is undefined), then by definition std::ptrdiff_t(array) will always have the lower 8bits be zero.
